Lets assume we have parallel wavefronts in a glass of water:
and we put an inclined rod on the water surface:
related to a very small inclining, Vy velocity is greater or much greater then Vx (Vy means, wavefronts' contact-making speed on the rod)
Now lets assume environment is space and the waves are of electro-magnetic ones: would Vx be smaller than c? Would Vy and Vx be equal? I dont think Vy would be greater than c. What do you think?
Assume inclined rod is just a metal rod and photo-electric effect is intact.